Getting my little monitor to work

[David Rutherford]

I purchased a little (oscilloscope?) monitor (5" screen) at a local
electronics supply store and am trying to get it to work. It came with a
mostly unreadable schematic that, according to a local TV repairman, is
not the correct one.

The manufacturer of the monitor is not printed anywhere on it, as far as
I can tell, so I can't contact them to get the correct schematic.
However, a schematic might not be necessary for what I need to do.

What I'm trying to do is get the electron gun to direct the electron
beam at the center of the screen. First, though, I need to find out how
to get it to operate. It's just a crt connected to a circuit board and
metal frame - no on/off switch. There's a 10-pin terminal on the circuit
board, but I don't know which pins are for what. There are also controls
for video center, v-hold, v-height, v-lin, and sub-bright.

Any help would be appreciated. Thanks.

Dave Rutherford

 

[Rich Andrews]

I purchased a little (oscilloscope?) monitor (5" screen) at a local
electronics supply store and am trying to get it to work. It came with a
mostly unreadable schematic that, according to a local TV repairman, is
not the correct one.

The manufacturer of the monitor is not printed anywhere on it, as far as
I can tell, so I can't contact them to get the correct schematic.
However, a schematic might not be necessary for what I need to do.

What I'm trying to do is get the electron gun to direct the electron
beam at the center of the screen. First, though, I need to find out how
to get it to operate. It's just a crt connected to a circuit board and
metal frame - no on/off switch. There's a 10-pin terminal on the circuit
board, but I don't know which pins are for what. There are also controls
for video center, v-hold, v-height, v-lin, and sub-bright.

Any help would be appreciated. Thanks.

Dave Rutherford

I am not sure what you inteded purpose is, but there is a fair amount of
information you are going to have to verify. I would start with a pinout
of the CRT, a verification of the existence of a power supply. and then
determine if the unit runs on 12 VDC, 120 VAC or some other voltage. This
can be a rather tedious chore. If it is as somple as you say it is, it
sounds like there is not power supply. If you don't have a power supply
for the beast, then it is only good for parts AFAIC.

r

 

[A E]

I purchased a little (oscilloscope?) monitor (5" screen) at a local
electronics supply store and am trying to get it to work. It came with a
mostly unreadable schematic that, according to a local TV repairman, is
not the correct one.

The manufacturer of the monitor is not printed anywhere on it, as far as
I can tell, so I can't contact them to get the correct schematic.
However, a schematic might not be necessary for what I need to do.

What I'm trying to do is get the electron gun to direct the electron
beam at the center of the screen. First, though, I need to find out how
to get it to operate. It's just a crt connected to a circuit board and
metal frame - no on/off switch. There's a 10-pin terminal on the circuit
board, but I don't know which pins are for what. There are also controls
for video center, v-hold, v-height, v-lin, and sub-bright.

Any help would be appreciated. Thanks.

Dave Rutherford

Betcha what you have there is a old Motorola style black and white 5 inch video
chassis. You need to feed it power, video and separate syncs. I think it needs
12VDC or some such. I even have one lying around, but I can't find it right now.
I had a schematic somewhere on how to hook it up... I'll try to find it.

 

[Harvey White]

Thanks, Rich. I actually have two of them - each one with a CRT from a
different manufacturer. One CRT is made by Matsushita, the other is made
by Toshiba. There is no power supply with them - just the metal frame,
circuit board, and CRT.

The electronics store had a schematic and a monitor circuit card detail
laying with the monitors (these, apparently, weren't the right ones,
though, since the solder lines don't match). On the monitor circuit card
detail, however, a + 12V power source was called for. I'll try to draw
it here from what I can make out (it's a little blurred),

------ system gnd
------ }
------ } optional remote brightness control
------ }
------ special application
------ horiz. drive in
------ + 12V in
------ video in
------ vert. drive in

------ system gnd

Are these standard pin assignments or do they usually differ from unit
to unit? Also, what kind of 'video in', if any, would I need if I just
want to have a constant intensity electron beam always pointing at the
center of the screen (no modulation)?

Whether they are standard assignments I cannot say. However, these
are not oscilloscope monitors, they are television monitors. They
must scan, and you cannot have a constant intensity electron beam
pointing at the screen.

Vertical sweep is always on, and is fixed at 60 Hz. Horizontal sweep
is generated from an external oscillator, and is used to derive the
high voltage.

Because the horizontal sweep is driven, the components in the monitor
can be damaged with improper drive.

These were made to be driven directly from a CRT display controller
chip, such as the Motorola 6845 or the 6847. Video can be a TTL
level video, I think, and the drive signals can also be TTL level.

Since the 6845 and 6847 (for example) do not put out the proper
signals without programming, this monitor is designed to be the
display for a system that has a microprocessor, one of the two display
chips, and enough programming to make it work right.

It will not work with your computer unless you can provide it with the
right drive signals, and at the right frequency. Even then, it will
work with only the lowest resolution and in black and white.

Harvey

 

[Bill Janssen]

If you have an old XT computer, the cga connector will have the H drive, V drive

and at least one video connection. You may need a "pot" connected to the three
terminals for the "brightness" control. I would use about 100KOhm for the pot.

The schematic may not be for your unit but the design was pretty standard
so it won't be far off.

Bill K7NOM

Oh yes another thing. I think you have to have the H drive to get the high voltage
for the CRT.

Bill K7NOM

 

[David Rutherford]

Whether they are standard assignments I cannot say. However, these
are not oscilloscope monitors, they are television monitors. They
must scan, and you cannot have a constant intensity electron beam
pointing at the screen.

Vertical sweep is always on, and is fixed at 60 Hz. Horizontal sweep
is generated from an external oscillator, and is used to derive the
high voltage.

Because the horizontal sweep is driven, the components in the monitor
can be damaged with improper drive.

These were made to be driven directly from a CRT display controller
chip, such as the Motorola 6845 or the 6847. Video can be a TTL
level video, I think, and the drive signals can also be TTL level.

Since the 6845 and 6847 (for example) do not put out the proper
signals without programming, this monitor is designed to be the
display for a system that has a microprocessor, one of the two display
chips, and enough programming to make it work right.

It will not work with your computer unless you can provide it with the
right drive signals, and at the right frequency. Even then, it will
work with only the lowest resolution and in black and white.

Harvey

I think putting all of your valuable suggestions to work might be a bit
much for my meager electronics abilities. I may have to try some other
way of doing what I need to do. Thanks, Harvey, for all your help.

Dave

 

[David Rutherford]

If you have an old XT computer, the cga connector will have the H drive, V drive

and at least one video connection. You may need a "pot" connected to the three
terminals for the "brightness" control. I would use about 100KOhm for the pot.

The schematic may not be for your unit but the design was pretty standard
so it won't be far off.

Bill K7NOM

Getting the monitor to work may be a little to much for me, due to my
lack of electronics knowledge. I'll give it a try until I reach the
point of diminishing returns (or diminishing patience). Thanks for all
the help, Bill.

Dave

 

[Michael Black]

Getting the monitor to work may be a little to much for me, due to my
lack of electronics knowledge. I'll give it a try until I reach the
point of diminishing returns (or diminishing patience). Thanks for all
the help, Bill.

Dave

Keep in mind that it's not going to do what you want. It's not an
oscilliscope, it's a video monitor. Only by adding external video
circuitry will you get your dot in the middle of the screen (and
since you didn't really say what you wanted the dot for, likely you'll
need more circuitry after that).

An oscilliscope is directly driven, so if you apply a signal to
the horizontal plates, the dot will move horizontally, the direction
defined by the polarity of the input signal. The same with the vertical
deflection.

With a monitor, that "dot" is constantly being deflected around
the screen, vertically, then down to the next line, and so forth.
The deflection is done with coils, and you won't get much if you
stop that scanning.

Michael

 

[James Sweet]

Keep in mind that it's not going to do what you want. It's not an
oscilliscope, it's a video monitor. Only by adding external video
circuitry will you get your dot in the middle of the screen (and
since you didn't really say what you wanted the dot for, likely you'll
need more circuitry after that).

An oscilliscope is directly driven, so if you apply a signal to
the horizontal plates, the dot will move horizontally, the direction
defined by the polarity of the input signal. The same with the vertical
deflection.

With a monitor, that "dot" is constantly being deflected around
the screen, vertically, then down to the next line, and so forth.
The deflection is done with coils, and you won't get much if you
stop that scanning.

Michael

Well it's possible to wire a choke in place of the yoke on the chassis to
get the HV, then you can externally drive the deflection coils, but
oscilloscopes use electrostatic deflection, the electromagnetic deflection
on a normal CRT is very limited in bandwidth and not very linear. You can
get some interesting patterns but nothing that even comes close in
usefulness to the old Heathkit, Eico and similar low bandwidth oscilloscopes
that show up at fleamarkets and on ebay for $10 or so fairly often. Also if
the dot sits in the middle for even a fraction of a second at full
brightness it'll burn a hole in the phosphor.

 

[Rich Andrews]

it.

That would be great, thanks A E.

Dave

I am not sure why you would want a single high intesity dot in the center
of the screen, but if you would take the yoke off the crt, that would stop
any sweep and you would have a single dot in the center.

r

 

[A E]

That would be great, thanks A E.

Dave

http://www.dfpresource.org/monitor.png

Just be sure it's the same thing... According to my inventory the actual monitor is
buried two boxes deep...
As others have said, this is a video monitor.

 

[David Rutherford]

I am not sure why you would want a single high intesity dot in the center
of the screen, but if you would take the yoke off the crt, that would stop
any sweep and you would have a single dot in the center.

That sounds like it's probably the easiest way to concentrate the beam
at the center of the screen. I didn't want to bore anybody with the
details, that's why I didn't mention my reasons for wanting to center
the beam. I'm actually using it for a physics experiment.

Dave

 

[David Rutherford]

http://www.dfpresource.org/monitor.png

Just be sure it's the same thing... According to my inventory the actual monitor is
buried two boxes deep...
As others have said, this is a video monitor.

Thanks, A E. I'll check my monitor against your schematic.

Dave

 

[Sam Goldwasser]

That sounds like it's probably the easiest way to concentrate the beam
at the center of the screen. I didn't want to bore anybody with the
details, that's why I didn't mention my reasons for wanting to center
the beam. I'm actually using it for a physics experiment.

Some people will pay a lot more attention to postings if they include the
reasons, not just the immediate needs.

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[David Rutherford]

Some people will pay a lot more attention to postings if they include the
reasons, not just the immediate needs.

And some people will pay a lot _less_ attention if they include the
reasons :^).

Dave